Pulsato rotors of the general type shown in Schwendener's patent have been used extensively. There are two basic modes of use. In the so-called free standing organization illustrated in the Schwendener patent, the pulsato rotor is mounted between spaced panels or partitions in a speaker cabinet. A speaker is mounted on one panel in line with the rotor axis but on the opposite panel side. The speaker registers via a large opening with the throat of the sound channel. In the so-called built-in organization illustrated in U.S. Pat. No. 3,245,284 to Donald J. Leslie issued Apr. 12, 1966 and entitled ROTOR DRIVE FOR PULSATO APPARATUS, the pulsator rotor is mounted on one side of a single panel or board while the speaker is mounted on the other side. In order to provide outboard support for the pulsato rotor, a generally U-shaped yoke or bracket is mounted on the panel. The panel together with the pulsato rotor and speaker is typically then mounted by an organ manufacturer in the console. The organ manufacturer is ordinarily responsible for back enclosure of the speaker so that the pulsato effects are not diluted by back radiation.
In addition to the problem of proper back enclosure of the speaker for full strength production of pulso, there have been certain noise problems in the pulsato unit of this general type. One noise is a flutter effect due to the rather substantial width of the yoke or bracket. Thus the yoke or bracket serves as a baffle or reflector that imposes a certain acoustic impedance that recurs twice every revolution. A slight, but objectionable flutter or buffeting takes place.
Another problem is the propogation and mechanical amplification of shaft and bearing noises that are most noticeable at low speeds and during speed changes of the rotor. Noises due to belt slippage and lateral movement are controlled by adjustment of the motor bracket and possible replacement of the pulley belt. In the past, a complex noise isolation pivoted motor bracket arrangement was provided that was not always stable in certain panel orientations.
The primary object of the present invention is to provide a simplified pulsato rotor that not only has improved musical characteristics in terms of noise reduction, flutter elimination and back speaker radiation, but which also has improved mechanical characteristics in terms of low weight, ease of assembly, standardization of parts, reduction in number of parts, and ease of pulley adjustment.